Direct sequence spread spectrum (DSSS) technologies allow the energy of a broadcast signal to be spread across a relatively wide frequency range through application of a digital code. DSSS technologies are widely used in modern wireless communications. Many conventional cellular phones, for example, make use of code division multiple access (CDMA) technologies that allow multiple transceivers to share a common channel through the use of unique digital codes applied to communications sent and received by each transceiver.
Spread spectrum signals frequently resemble noise signals in that they have a relatively large number of different frequency components, each with relatively low power. DSSS signals can be very difficult to identify in a received signal, then, because DSSS signal components tend to resemble the background noise. Receivers that have access to the digital code used to modulate a broadcast signal, however, can readily recreate the transmitted message using the code. If the receiver does not have access to the spreading code, it can be extraordinarily difficult to receive the broadcast message, or even to identify that a signal is present in the background noise, especially when the particular spreading code used to modulate the DSSS signal is unknown to the detecting party.
Detecting and locating a particular CDMA or other DSSS signal within an area, then, can be relatively difficult, particularly when the spreading code associated with the signal is not known. Because CDMA signals are typically spread across multiple frequencies and transmitted at the same time and within the same portion of the RF spectrum as other DSSS signals, conventional time and frequency-based de-multiplexing techniques can be of little use in isolating and identifying such signals.
Despite these challenges, interest nevertheless remains in identifying and/or geolocating DSSS transmissions within a geographic region or area. It is therefore desirable to create systems and techniques for detecting and/or locating DSSS transmitters. It would be further desirable that such systems and techniques be able to identify DSSS transmitters without a priori knowledge of the spreading code used by the transmitter. These and other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background section.